Sample splitting

The use of a fused silica capillary column for the GC analysis of the neutral oil extract has provided the means for improving the resolution of components in a more inert system. The sultones are determined by temperature-programmed GC over CP-Sil-5 CB (methyl silicone fluid) in a 25 m x 0.2 mm fused silica capillary column using nonadecane as internal standard. A sample split ratio of 1 100 is recommended for a 3-pl injection. 

Unfortunately, the preset split flow ratio is only an approximate indication of the sample split ratio. The latter depends in a complex way on many parameters, including the range of sample volatilities, sample solvent, volume of sample injected. 

When solid phase synthesis is combined with sample splitting, there is a particularly useful outcome.60 The solid support can be used in the form of small beads, and... 

The U-tube was developed to simplify the recovery of fluids from deep boreholes and allow flexibility for post-sampling analysis (Freifeld et al. 2005 Freifeld Trautz 2006). In particular, the ability to repeatedly collect large volume multiphase samples into high pressure cylinders facilitates both real-time field analysis as well as acquisition of sample splits for future laboratory based analysis. 

For most of the laboratories, additional quality control (QC) samples were inserted within each batch of samples sent. These included sample site duplicates, sample splits for analytical duplicates, a suite of USGS-prepared standard reference materials (SRMs), and... 

The procedure used for day-to-day monitoring utilizes a single real sample (usually a composite of previously analyzed samples) split into two aliquots labeled A and B. These samples are carried through the analytical procedure together with the unknowns. 

The glass liner is slowly contaminated by nonvolatile and decomposed samples and must be replaced periodically. For splitless injection, the glass liner is a straight tube with no mixing chamber. For dirty samples, split injection is used and a packing material can be placed inside the liner to adsorb undesirable components of the sample. 

The last major decision is how to inject the sample. Split injection is best for high concentrations of analyte or gas analysis. Quantitative analysis is very poor Less volatile components can be lost during injection. Split injection offers high resolution and can handle dirty samples if an adsorbent packing is added to the injection liner. Thermally unstable compounds can decompose during the high-temperature injection. 

Spectral subtraction and spectral search aid the identification of evolved gases, which are often a mixture of products. Nevertheless, for unambiguous identification of unknown volatiles more powerful methods are required. Jansen and co-workers [86] have incorporated a parallel mass spectrometer onto the FTIR stage of a thermogravimetry-FTIR (TG-FTIR). The sample is thermally decomposed by TGA and the products collected in a Tenax (absorbent charcoal) trap. After desorption, the products are separated by a GC and the sample split, with 99% going to the IR spectrometer and 1% to the mass spectrometer. 

Pipettes and pipette balls used for sample splitting... 

OPCW procedures require sample splitting into eight portions, which are distributed as follows ... 

Sample splitting is performed at the OPCW onsite laboratory (if available) except for highly toxic samples, which require decontamination and hot line procedures. These samples (e.g. neat CW agent) are split directly after sampling into eight small subsamples. This reduces the risk of contamination of the on-site laboratory, especially the fume hood. Afterwards, only one split sample of approximately 100 xL (see Table 3) will be handled in the fume hood for sample preparation. 

On their arrival at the OPCW Laboratory, all seal numbers and the end pattern of the fiber-optic seals will be compared to the seal numbers and photographs received from the inspection site, if so requested in the presence of an ISP representative. Unpacking will be performed in a dedicated area for handling of authentic samples in the OPCW Laboratory. The vials containing the authentic sample splits will be weighted but left closed and sealed as received from the inspection site. For dispatch to each designated laboratory, one authentic sample split is packed together with a pre-analyzed control sample and the respective matrix blank in a transport container in the same manner as described above. A... 

All documents related to and created during onsite sampling, sample splitting, sample preparation, and analysis are attached to the on-site analysis report (see below). The on-site analysis report is part of the report created by the IT concerning the inspection activities and subject to the same confidentiality regime as the report itself. Under no circumstances are any of these documents sent together with samples off-site. The on-site analysis report has to provide data to validate the method as well as the analysis result in accordance with OPCW procedures and the Quality System requirements. 

The essential parts of a gas chromatograph as shown in Figure 8.1 are carrier gas, flow or pressure regulator, injection port or valve, column, and detector. Usually there are three heated zones, each separately controlled, for the inlet area, the column, and the detector. Connections between these heated zones must also be kept hot enough to prevent condensation of analytes in them. Chromatographs designed for OT columns usually have additional features a more elaborate injection port that allows for sample splitting and a provision for some additional make-up gas for the detector. Information about commercial instruments can be found in the review by Bayer.3... 

Figure 8.3. Inlet designed for OT columns and sample splitting. Courtesy of Parian Instruments.

Early calibration materials were often pollen since these have a very narrow size range. Arguments persist as to whether these swell in liquids or change size over time. Polymer latices are also available as calibration material. When instruments are used regularly to test a limited range of products the product itself can be used for calibration purposes. Thus a manufacturer of titanium dioxide may set aside an easily dispersed, stable sample for sample splitting and subsequent use for instrument evaluation. 

As most of the sizing methods are hmited to small sample sizes, an important prerequisite to accurate particle-size analysis is proper powder sampling and sample splitting (upcoming ISO 14488, Particulate Materi —Sampling and Sample Splitting fir the Determination of Particulate Properties). 

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